The response of superior colliculus cells to stimulus movement was compared in front of the stationary eye with the response to stimulus movement generated by eye movement. Most cells responded to very high stimulus velocities in front of the stationary eye. The majority of these cells did not respond when an eye movement swept the receptive field over a stationary stimulus. This differentiation is present when the background illumination is reduced. For these cells, a suppression of background activity is present following eye movements made in total darkness, indicating the presence of an extraretinal signal. The time course of this suppression matches the time at which visual effects would reach the colliculus. These cells in the superior colliculus receive an extraretinal input which permits them to differentiate between real stimulus movements and stimulus movements resulting from the monkey's own eye movements. This differentiation would provide an uncontaminated visual movement signal and facilitate the detection of real movement in the environment.